1. Field of the Invention
The present invention is directed to linear functional polymers, especially linear functional polymers having randomly repeating units. The present invention is further directed to processes for making these linear functional polymers.
2. Description of the Related Art
Polyethylene is the synthetic polymer produced in the highest volume and is better considered a class of polymers rather than a single polymer, since the types of polyethylene produced in different ways offer an enormous range of physical properties. Altering the size and distribution of alkyl branches and incorporating polar functional groups into the polymer are two common methods of controlling the properties of polyethylene.
Alkyl branches in polyethylene can consist of both long-chain branches (LCB), which are branches of sufficient length (typically six or more carbon atoms) such that they cannot be distinguished by 13C nuclear magnetic resonance, and short chain branches (SCB), which are branches having typically less than six carbon atoms. While long chain alkyl branching can be beneficial for the processing of polyethylenes, certain alkyl branches—particularly SCB—can negatively affect critical properties such as melting point (Tm), glass transition (Tg) temperature, crystallinity, strength, thermal stability, and optical clarity. Conversely, the presence of polar functional groups as sidechains in the polymer can improve desired properties such as impact strength, adhesion, dyeability, printability, solvent resistance, melt strength, miscibility with other polymers, and gas barrier properties.
However, when short chain branching is present in functional polyethylenes, SCB effects tend to dominate certain polymer properties, for example Tm. Thus, the fundamental effects of the polar substituents themselves are not well understood and cannot be independently exploited. It is therefore desirable to prepare polyethylenes that contain polar functional groups but lack alkyl branching, particularly SCB. It is also desirable that the functional groups be attached as sidechains directly, or as closely as possible, to the polymer backbone, rather than being separated from the polymer backbone by long alkyl branches or chains. At low levels of polar functional groups, the physical properties of high-density polyethylene (HDPE), including rigidity, high modulus and strength, would be expected to be retained while adding the benefits of polar functional groups. Conversely, at higher polar functional group levels, the polymer structure is disrupted by the polar groups and has physical properties that differ more from those of polyethylene.
Copolymers of ethylene with olefin monomers bearing a polar functional group substituent (i.e., H2C═CHR, where R is a polar functional group; hereafter referred to as “polar vinyl monomers”) have traditionally been prepared by high-temperature, high-pressure free radical polymerization processes similar to those employed to produce low-density polyethylene (LDPE). Such high-temperature free radical polymerization of ethylene and polar vinyl monomers always produces short- and long-chain alkyl branching, due to the same mechanisms which lead to branching for the free radical homopolymerization of ethylene to LDPE, and other mechanisms involving the functional comonomer.
In high-pressure free-radical copolymerization, functional polyethylenes are prepared by the copolymerization of ethylene (E), CH2═CH2, with a polar vinyl monomer (V), CH2═CHR1. Each E unit contributes two CH2 groups to the polymer structure. Each V unit contributes one CH2 group and one CHR1 group to the polymer structure. For a polar vinyl monomer CH2═CHR1, the olefinic carbon of the ═CHR1 group is referred to as the “head” (H) of the molecule, while the olefinic ═CH2 carbon is referred to as the “tail” (T) of the molecule.
The copolymerization of ethylene and polar vinyl monomers produces polymer structures in which any sequential combination of E and V units is possible. These include structures in which two V units are attached directly to each other (“VV dyad”), as well as structures wherein V units are separated from each other by some intervening number, k, of E units. Both types of structures may be present in one polymer. Additionally, the polar vinyl monomer may be connected through either its “head” or “tail,” such that the polymer structures produced are of the type:
where k equals an integer greater than or equal to 0. All of these structures may be present in one polymer.
For the case of a VV dyad (k=0), connectivity occurring between the V units through two ═CHR1 carbons is referred to as a “head to head” linkage. Connectivity occurring between a=CHR1 carbon and a=CH2 carbon is referred to as a “head to tail” linkage. Connectivity occurring between two ═CH2 carbons is referred to as a “tail to tail” linkage. For the general case where k is greater than or equal to 1, these three patterns are referred to herein as pseudo-head-to-head (HH), pseudo-head-to-tail (HT), and pseudo-tail-to-tail (TT) linkages, respectively.
The run length, r, is defined as the number of CH2 units intervening between each —CH(R1)— unit in the polymer. The possible values of this quantity may be mathematically represented by three formulas corresponding to the pseudo-head-to-head, pseudo-head-to-tail, and pseudo-tail-to-tail connectivity of the polar vinyl monomer units:rHH=2krHT=2k+1rTT=2k+2where k is an integer greater than or equal to 0.
The allowed values for r are thus:rHH=0, 2, 4, 6, 8, 10 . . .rHT=1, 3, 5, 7, 9, 11 . . .rTT=2, 4, 6, 8, 10, 12 . . .
Since all of these structures may be present in one polymer, the overall allowed values for r, rtotal, are:rtotal=rHH+rHT+rTT therefore,r=0, 1, 2, 3, 4, 5, 6 . . .
Copolymers of ethylene and polar vinyl monomers prepared by free-radical copolymerization thus possess a continuous run length distribution, in which the run lengths, r, present in any one polymer vary, and can equal any integer greater than or equal to 0. The actual values of r present in a polymer are statistically determined by monomer feed and reactivity ratios.
Certain metal-based catalysts are known to copolymerize ethylene with polar vinyl monomers via a coordination-insertion mechanism to yield functional polyethylenes having different branching patterns and polar functional group placements than polymers produced by free-radical copolymerization. For example, nickel diimine complexes developed by Johnson, et al., Polym. Mat. Sci. Eng. 2002, 86, 319, are capable of copolymerizing ethylene and methyl acrylate. However, the polymers formed are not linear and contain up to 95 alkyl branches per 1000 carbons. Copper bis-benzimidazole complexes discovered by Stibrany, et al. in U.S. Pat. No. 6,417,303 can also copolymerize ethylene with acrylates or vinyl ethers to give “substantially linear” copolymers having up to 17 C1–C6 alkyl branches per 1000 carbons. For these coordination-insertion copolymers, any sequential combination of E and V units is possible, including VV dyads. The copolymers possess a continuous run length distribution in which the run lengths, r, present in any one polymer vary, and can equal any integer greater than or equal to 0.
Drent, et al., Chem. Commun. 2002, 744, have reported phosphine-ether-ligated palladium copolymerization catalysts that can be used to produce linear ethylene/acrylate copolymers. These polymers also possess a continuous run length distribution in which the run lengths, r, may vary, except that no double acrylate-acrylate insertions (VV dyads) are observed as determined by nuclear magnetic resonance. Thus, for these polymers, the permitted run lengths are:rHH=2krHT=2k+1rTT=2k+2where k is an integer greater than or equal to 1; and the overall allowed values for r are:r=2, 3, 4, 5, 6 . . . .
These VV-dyad-free copolymers disclosed in the art, thus, possess a continuous run length distribution in which r is an integer greater than or equal to 2.
Free-radical and coordination-insertion copolymerization techniques, therefore, provide methods for producing substantially linear polymers having continuous run length distributions. These techniques allow for the adjustment of composition (mole percent polar vinyl monomer present in the copolymers) by the technique of varying monomer feed ratios and reaction variables such as temperature and pressure. However, free-radical and coordination-insertion copolymerization techniques do not provide a method to produce linear functional polymers in which the minimum value of r is an integer greater than 2. These techniques also only provide statistical control of run length.
Although great progress has been made in tailoring polyolefin properties by control of composition, branching and tacticity, current catalyst technology does not allow for similar manipulations of run length distributions. Run length distribution effects play an important role for determining polymer crystallinity and, therefore, mechanical properties such as modulus and melting point. For example, in an ethylene-propylene copolymer, the methyl substituent of an isolated propylene unit incorporated into the polymer chain may fit into the polymer's crystal lattice, producing no adverse effect on crystallinity. However, a larger branch structure formed by the two proximal methyl substituents of a propylene-propylene dyad may not fit into the crystal, causing a reduction in crystallinity and melting point. See Ke, B., J. Polym. Sci., 1962, 61, 47. In general, polyethylenes having longer run lengths show higher crystallinity. Thus, it is desired to control run length distributions such that polymers with longer run lengths are produced. It is also desired to control run lengths in a non-statistical manner such that polymers completely free from dyads and other short run length sequences can be obtained.
Another desirable feature is to produce a polyethylene having not only large run lengths, but a narrow run length distribution. By this it is meant, for example, a polymer having an average run length of 40 but containing a small range of run lengths distributed around this average value, e.g., from 38 to 42 (r=40±2). Conversely, a polymer having an average run length of 40 but with a broad run length distribution would possess run lengths from, for example, 10 to 70 (r=40±30). Polymers having continuous run length distributions are a subset of polymers having broad run length distributions.
Polymers in which only one run length is present (i.e., r=40) are referred to as having monodisperse run length distributions. Polymers in which the only run lengths present are multiples of a single value (i.e., 40, 80, 120, etc.) are referred to as having periodic monodisperse run length distributions. Polymers in which a small distribution of run lengths are present (i.e., r=40±2) are referred to as having narrow run length distributions. Polymers in which the only run lengths present are multiples of narrow distributions (i.e., r=40±2, 80 ±2, 120±2 . . . ) are referred to as having periodic narrow run length distributions.
Polymers having monodisperse, narrow, and periodic run length distributions, collectively referred to as polymers with regular run length distributions, possess different properties compared with polymers having less regular distributions, because the former's regular structures can be used to control crystalline morphology. For polyolefins having broad run length distributions, morphology (i.e., lamella size) is controlled by the kinetics of the crystallization process. However, for polymers with more regular architectures, morphology can instead be dictated by microstructure. For example, polymers with regular run length distributions are likely to form lamellae with thicknesses equivalent to the run length, in which each branch can be efficiently accommodated at the surface of the lamella (in a hairpin turn of the chain) rather than having some branches separated by shorter run lengths forced inside the lamella as defects. See Ungar, G., Zeng, X. B., Chem. Rev., 2001, 101, 4157. Thus, control of run length allows for control of crystalline morphology, and, therefore, for control of polymer physical properties.
Control of run length distribution is an important issue for aliphatic polyolefins, but it is even more critical for functionalized polyethylenes. This is due to the influences that the polar functional groups can exert on polymer crystallinity. For example, polymers possessing hydroxyl substituents might be expected to undergo hydrogen bonding of these groups in the polymer crystal structure. Hydrogen bonding may be more facile for polymers with regular run length distributions (in which the hydroxyl substituents are present at regularly spaced distances), and thus may exert a greater influence on properties than for polymers with a broader distribution of hydroxyl groups. This is particularly true for linear functional polyethylenes, in which the influences of the functional groups are not overshadowed by influences of alkyl branches.
Polyethylenes having monodisperse run length distributions of polar functional group substituents have been prepared using acyclic diene metathesis (ADMET) polymerization. See Valenti, et al., Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem., 1996, 37(2), 325; Valenti, et al, Macromolecules, 1998, 31, 2764; Wagener, et al., Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem., 1998, 38(1), 719; Watson, et al., Macromolecules, 2000, 33, 5411; Watson, et al., Macromolecules, 2000, 33, 8963; Watson, et al., Macromolcules, 2000, 33, 3196; Schwendeman, et al., NATO Sci. Ser. II. Math., Phys., Chem., 2002, 56, 307, all of which are incorporated by reference herein. This technique involves the metathesis homopolymerization of an acyclic α,ω-diene having a central, symmetrically placed polar functional group substituent, followed by hydrogenation of the olefins in the resultant polymers. The functional polyethylenes produced are rigorously linear in that they possess zero alkyl branches in the chain structure. Polymers bearing acetate, ketone, hydroxyl, —CO2CH3, and —CO2CH2CH3 groups with run lengths of 18, 20, 22, and 26 are known. These polymers have compositions analogous to linear copolymers of ethylene and polar vinyl monomers (e.g., vinyl acetate, vinyl alcohol, methyl acrylate, ethyl acrylate, among others) containing 7.4 mol % and above of the polar vinyl monomer. For this technique, control of polymer composition can only be achieved by varying the size of the functional acyclic α,ω-diene monomer used. No copolymers with less than 7.4 mol % polar have been prepared in the art. At the composition range of 7.4 mol % polar vinyl monomer and greater, the ADMET polymers with monodisperse run length distributions possess much lower melting points than alkyl-branched copolymers with similar compositions prepared by free radical polymerization processes. This is disadvantageous because many uses of polyethylene in the art typically favor high melting points.
A variety of rigorously linear polyethylenes and polyalkenamers (i.e., polyethylenes containing olefinic groups in the main chain) having narrow run length distributions of polar functional group substituents have been prepared using ring opening metathesis polymerization (ROMP). See McLain, et al., Polym. Mat. Sci. Eng., 1997, 76, 246; Stumpf, et al., J. Chem. Soc. Chem. Commun., 1995, 1127; Noels, et al., NATO ASI Ser. C: Math., Phys. Sci., 1998, 506, 29; Hillmyer, et al., Macromolecules, 1995, 28, 6311; Korean Patent No. KR349626 and Korean Application No. KR2001036073 to Cho, et al.; International Patent Application Number PCT WO03/078499 to Weaver, et al.; and International Application Number PCT WO00/18579 and U.S. Pat. No. 6,203,923, both to Bansleben, et al., all of which are incorporated by reference herein. This process involves the homopolymerization of cyclooctene monomers having a polar functional group substituent at the 5-position, and subsequent hydrogenation or reduction of the olefins in the resultant polymer, which has a composition equivalent to 25 mol % polar vinyl monomer. The 5-substituted cyclooctene monomer can bond in a head-to-head (r=6), head-to-tail (r=7), or tail-to-tail (r=8) fashion, giving overall allowed run lengths of r=6, 7, 8 carbons. Cho, et al. (Korean Pat. No. KR349626 and Korean Appln. No. KR2001036073) have also disclosed the ROMP homopolymerization of cyclododeca-4,8-dienyl acetate to produce polyethylenes containing 16.6 mol % vinyl alcohol or vinyl acetate.
ROMP homopolymerization of 5,6-disubstituted cyclooctenes can be similarly carried out to produce linear polyethylenes having vicinal dihydroxyl substituents (—CH(OH)CH(OH)— structures) equivalent to head-to-head vinyl alcohol dyads. See International Application Numbers PCT WO99/50331 and PCT WO00/18579 and U.S. Pat. Nos. 6,153,714, 6,506,860 and 6,203,923, all to Bansleben, et al.; Scherman, et al., Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem., 2003, 44(1), 952, all incorporated by reference herein. These polymers have a composition equivalent to 50 mol % vinyl alcohol and a monodisperse run length distribution, with a six carbon run length separating each —CH(OH)CH(OH)— structure (r=6).
Many other ROMP homopolymerization processes giving polymers with greater than 25 mol % polar vinyl content are known. However, ROMP homopolymerization to produce linear functional polymers having polar vinyl contents of less than 16.6 mol % are not exemplified in the art. ROMP of large cyclic monomers bearing polar functional substituents in the appropriate positions to produce polymers with narrow run length distributions are also not known in the art. Rigorously linear functional polyethylenes containing 16.6 mol %, and higher, polar vinyl contents can also be prepared by functionalization of preformed polyoctenamers and polydodecenamers. McLain, et al., Polym. Mat. Sci. Eng., 1997, 76, 246.
The ROMP copolymerization of substituted cyclooctenes with cycloalkenes has been used in a few instances to produce substituted polyethylenes or polyalkenamers. Breitenkamp, et al., Macromolecules, 2002, 35, 9249, and Polym. Prepr. Am. Chem. Soc. Div. Polym. Chem. 2002, 43(2), 725, have copolymerized cyclooctene with a substituted cyclooctene bearing a long-chain polyethylene glycol substituent. Maughton and Grubbs, Macromolecules, 1996, 29, 5765, copolymerize cyclooctadiene with 5-methacryloyl-1-cyclooctene to give methacryloyl-substituted polyalkenamers that can be cross-linked through the pendant vinyl functionality of the methacryloyl group. These polymers are also susceptible to incidental, unwanted cross-linking during the polymerization and purification process. Stevens, et al., Ann. Tech. Conf.—Soc. Plastics Eng., 2002, 60(2), 1854; Yang, et al., J. Polym. Sci. A: Polym. Chem., 2003, 41, 2107; and Stevens, et al., J. Polym. Sci. B: Polym. Phys., 2003, 41, 2062, all incorporated by reference herein, have copolymerized chlorocyclooctenes with cyclooctene to give chloro-substituted linear polyethylenes and polyalkenamers.
Thus, there is a need in the art to prepare polyethylenes containing polar functional groups which lack alkyl branching, particularly short-chain branching. There is also a need for rigorously linear functional polymers that are free of polar VV dyads. A further need exists for a method to control run length distributions in a non-statistical manner to make such dyad-free polymers having large, narrow run length distributions. Lastly, there is a need to make a polymer containing less than 7.4 mole % polar functionality.